1. Field of the Invention
The present invention relates to a metal pipe expander for uniformly expanding a metal pipe in its inner diameter.
2. Description of the Related Art
In a known conventional method for uniformly expanding of the inner diameter of a steel pipe of relatively short length, the rear end of a tapered metal pipe expander (mandrel) shaped like a short cylinder, which has been inserted into a steel pipe, is pushed inward with mechanical means such as a shaft to move forward the metal pipe expander in the axial direction within the steel pipe, or the metal pipe expander is rotated while being moved, whereby the steel pipe is expanded.
However, the pipe expanding method does not function well in expanding a long metal pipe, e.g., an oil well pipe extending several hundreds meters to several kilometers. When the method is used for expanding such a long metal pipe, the shaft for driving forward the metal pipe expander suddenly buckles. For this reason, it is remotely possible to employ the expanding method. For this reason, to expand such a long metal pipe in diameter, the following pipe expanding method is used. Liquid, e.g., water, after pressurized, is supplied into the metal pipe. A liquid pressure generated is applied to the rear end face of the metal pipe expander, and the propel force caused by the liquid pressure drives forward the metal pipe expander, thereby expanding the steel pipe in diameter.
However, the liquid-pressure basis expanding method has also the following serious problem. During the expanding operation, the metal pipe is often broken (burst) at a position near the metal pipe expander located by the liquid pressure for driving forward the metal pipe expander. Particularly, in the case of the oil well pipe, if the bursting accident occurs at a deep place in the earth, it is impossible to repair the broken, long oil-well pipe unless it is dug out of the ground. This presents a serious problem.
It is an object of the present invention to provide a metal-metal pipe expander which can prevent the metal pipe from being broken by reducing a force exerting on the metal pipe during the pipe expanding operation.
To achieve the above object, the inventor of the present invention analyzed forces exerting on a metal pipe when the metal pipe is expanded by using the metal pipe expander. The analysis will be described with reference to FIG. 4. As shown, a metal pipe expander 41, shaped like a conic body, is inserted into a metal pipe 10, and moved forward (in the direction of an arrow X) for pipe expansion by a liquid pressure. At this time, an expanding force F acts on an expanded part 13 of the metal pipe 10, which is under deformation by the press fitting of the a conical surface 41a of the metal pipe expander 41. Also at this time, an expanded portion 10a of the metal pipe receives a tension T which has a direction coincident with a longitudinal direction of the pipe and corresponds to the propel force of the metal pipe expander 41, and an internal force R which results from a liquid pressure xe2x80x9cpxe2x80x9d causing the propel force. Those three forces act on an expansion-terminating position 14 of the pipe and therearound in a complex manner. As a result, excessive stress is generated and the pipe is easy to be broken thereat. This fact was found and confirmed by the inventor. Further, the inventor carefully examined the metal pipes broken when those pipes were expanded. From the examination, it was found that many broken pipes were broken while being greatly bent. From this fact, it is estimated the cause of the breakage of the metal pipe as follows: The deviation of the wall thickness of the metal pipe and the like cause the metal pipe to bend during its expanding operation. The bending of the metal pipe progressively grows. A great bending stress is locally generated and is added to the stress caused by the three forces including the expanding force F and the like. As a result, the metal pipe is easy to be broken.
The present invention was made based on the findings mentioned above, and prevents excessive stress from acting on the metal pipe by blocking the exerting of the internal force R on the expansion-terminating position 14 and therearound or by the internal force blocking and by restricting the bending of the metal pipe associated with the pipe expanding operation.
According to the present invention, there is provided a first metal pipe expander which is inserted into a metal pipe and driven to move in the axial direction of the metal pipe by a liquid pressure, wherein a cup shaped portion opened to the rear side, the outer surface of which is in slide contact with the inner surface of the metal pipe after it is expanded in diameter, is provided at the rear end of an expanding section with a conical portion of which the small diameter portion is directed to the front side.
In the description to follow, the term xe2x80x9cforexe2x80x9d side means the fore side as viewed in a direction in which the metal pipe expander advances when the pipe is expanded. The term xe2x80x9crearxe2x80x9d side means the side opposite to the fore side.
In the first metal pipe expander, a liquid pressure of pressurized liquid supplied into the metal pipe acts on the rear end of a cup shaped portion of the pressure receiving section of the metal pipe expander, to thereby drive and move forward the expanding section integral with the pressure receiving section to expand the metal pipe. At this time, the liquid pressure is sealed with a sliding contact portion between the outer surface of the cup shaped portion and the inner surface of the expanded metal pipe. Therefore, there is no chance that an internal force R caused by the liquid pressure acts on the inner surface of the metal pipe located on the fore side. Accordingly, the internal force R does not exert on the expansion-terminating position and therearound of the metal pipe. As a consequence, an excessive stress is not generated in the metal pipe.
One pressure receiving section may be used for the pressure receiving section located on the rear side of the expanding section. A plurality of the pressure receiving sections may be provided while being longitudinally and contiguously arranged as in the second metal pipe expander. In this case, even if, by wear of the outer surface of the cup shaped portion of the pressure receiving section, the sealing between it and the inner surface of the metal pipe is damaged, the sealing of the outer surface of the cup shaped portion of the pressure receiving section located on the fore side, reliably blocks application of the internal force R to the expansion-terminating position 14 and its near portion of the expanded metal pipe. In this regard, the construction of the second metal pipe expander is preferable. Further, during and after the pipe expanding operation, the metal pipe is supported at a total of three locations linearly arrayed, the expanding section and the plurality of cup shaped portions of the pressure receiving sections. Therefore, the bending of the metal pipe caused when the pipe is expanded is controlled to be extremely small. As a result, the breakage of the metal pipe owing to this bending is reliably prevented. In this respect, the construction of the second metal pipe expander is more preferable.
Also in the third metal pipe expander in which a guide portion is further provided between the expanding section and the pressure receiving section in a state that the guide portion is in slide contact with the inner surface of the metal pipe after it is expanded, during and after the pipe expanding operation, the metal pipe is supported at a total of at least three locations, the expanding section and one or the plurality (in the case of the second metal pipe expander) of cup shaped portions. Therefore, the bending of the metal pipe caused when the pipe is expanded is controlled to be extremely small. As a result, the breakage of the metal pipe owing to this bending is reliably prevented. In this respect, the construction of the third metal pipe expander is preferable.
In the fourth metal pipe expander in which a guide portion with a fitting part is further provided on the fore side of the expanding section, the fitting part being brought into press contact with the inner surface of the metal pipe at a position spaced apart from the expanding section, the fitting part of the guide portion is brought into press contact with the inner surface of the metal pipe before it is not yet expanded, so that an inclination of the axial line of the expanding section with respect to the axial line of the metal pipe not yet expanded is controlled to be extremely small. This technical feature also reduces the bending of the metal pipe by the pipe expansion, and prevents the breakage of the metal pipe owing to this bending. In this regard, the construction of the fourth metal pipe expander is preferable.